Luidiidae Family of Starfish

Phylogeny:  The Luidiid Sea Stars are members of the Luidiidae Family of Starfishes and in the Phylum Echinodermata, that is a large Phylum that includes Brittle Stars, Sea Cucumbers, Sea Lilies, Starfish and Urchins. The Echinodermata are of great scientific interest because, via fossil records, they have been dated to the Cambrian Age (over 500,000,000 years ago) with 7,000 living and 13,000 extinct individual species. They are in the Class Asteroidae and the Order Paxillosida.

Distribution:  Luidiid Sea Stars are found only in marine environments worldwide in tropical and temperate seas with 1,500 species known globally. There is only one genus, Luidia, which has forty-eight in the Luidiidae Family of which eight species are found along Mexico’s Pacific Coast. They are found on sand, mud, and muddy gravel substrate from the intertidal zone to depths up to 1,300 m (4,260 feet).

Morphology:  Luidiids characterized by having only one larval phase, compared to the two phases of other Orders within this Class, and an adult stage with 5-rayed radial symmetry. They have an unsegmented small flattened flexible central disk, that are covered with skin, with tapers arms that have a broad attachment point where the arms join the disc. They have a large mouth angle plates comprised of fused ambulacral ossicles. They lack an anus, and are unable to extrude their stomach like most other sea stars. They have sessile pedicellariae. Their tube feet are pointed and lack suckers which are used, along with their spines to borrow under the surface of the soft sediments in which they live. They have a unique water-vascular system that uses hydraulic power to operate a multitude of tined tube feet that are used in locomotion and food capture. Their tube feet lack suckers, but have double ampullae (bulb-like appendages that push water into tube feet, causing them to extend). The pedicellariae may be either stalked or sessile. They have a complete digestive system, but they lack a head, eyes, nervous system, or excretory system. The disc contains most of the organs, with the mouth on the ventral side and the anus and madreporite (entry plate for the water vascular system) on the dorsal surface. Luidiids reach up to 60 cm (23 inches) in diameter. While most sea stars can automize (self-amputate) their arms to avoid predation, Luidiidae Sea Stars can do so where the arm join the disc and at any point along the arm. They have the ability to regenerate amputated limbs. Sea Stars in the Luidiidae Family are often brightly colored.

Ecosystem Roles:  They scavenge carrion and detritus, scavenge carrion, or prey upon bivalves, crustaceans, gastropods, polychaetes, sea cucumbers, sea urchins, and other sea stars. In turn Luidiids are preyed upon by shore-birds, crabs, fish, and other sea stars.